Elucidating the effect of dietary neem (Azadirachta indica) on growth performance, haemato-biochemical, immunonological response, and anti-pathogenic capacity of Nile tilapia juveniles.

This investigation attempts to evaluate the effect of diet additives via aqueous or ethanolic herbal extracts from Azadirachta indica leaves on Nile tilapia, Oreochromis niloticus. Five dietary categories were assigned to the fish: the first category (N1, with no extract) was kept under control conditions; two categories contained aqueous extract (N2 (1.0 g/kg) and N3 (2.0 g/kg); and two categories contained ethanolic extract, N4 (1.0 g/kg) and N5 (2.0 g/kg), with each group being fed for 60 days. After the feeding trial, Aeromonas hydrophila was injected intraperitoneally into fish for 14 days; fish mortality was recorded during this period. The results showed that the fish-fed dietary A. indica significantly improved growth performance and intestinal health (digestive enzymes and intestinal morphology), especially in the N4 and N5 categories. However, N4 and N5 categories demonstrated a significant decrease in AST and ALT activities and an increase in total protein, serum albumin, globulin, growth hormone (GH), leptin hormone (LEP), hemoglobin, white blood cells, and hematocrit (P  < 0.05) in comparison with the control category (N1). Compared to the control category, the N4 and N5 categories have revealed a significant reduction in MDA activity and improvements in immunological activities (lysozyme, complement C3, and nitric oxide) and antioxidant enzymes (CAT, SOD, and GPX). Moreover, in tilapia-fed A. indica, the expression of IL-8, IL-1β, and Nf-κb genes was downregulated partially in the N4 and N5 categories than the control category. In contrast, the lysozyme, C3, GPX, and CAT genes were upregulated partially at N4 and N5 compared to the control category. Following the bacterial challenge, fish in the N4 and N5 categories also displayed the lowest fish mortality compared to the control category. The ethanolic extract displayed a more potent resistance against the parasite Cichlidogyrus tilapia in vitro than the aqueous and control categories, partially at 2 g/L. According to these findings, an ethanolic neem extract (2.0 g/kg feed) activates the immune system and antioxidant response in Nile tilapia fingerlings, improving growth and fish resistance to parasitic and bacterial infections.